Cold punchable laminates

ABSTRACT

Industrial cellulosic laminates which can be cold punched without appreciably cracking or shattering. The laminates are prepared from papers impregnated with a mixture of a carboxylated alkadiene interpolymer and a low molecular weight phenolformaldehyde resin.

United States Patent Inventor Ronald 1'1. Dahms Springfield, Mass.

Appl. No. 738,793

Filed June 21, 1968 Patented Dec. 14, 197 l Assignee Monsanto CompanySt. Louis, Mo.

COLD PUNCHABLE LAMINATES 2 Claims, No Drawings US. Cl 161/251,156/308,156/322, 156/331,156/334,156/335,161/252,16l/253,161/248,161/254,161/255,

1nt.Cl ..B32b 27 10,

B32b 27/30, c091 Field 01 Search 161/250,

Primary Examiner.1ohn T. Goolkasian Assistant ExaminerC. B. CosbyAttorneys-John W. Klooster, Arthur E. Hoffman and H. B.

Roberts ABSTRACT: Industrial cellulosic laminates which can be coldpunched without appreciably cracking or shattering. The laminates areprepared from papers impregnated with a mixture of a carboxylatedalkadiene interpolymer and a low molecular weight phenol-formaldehyderesin.

COLD PUNCHABLE LAMINATES BACKGROUND In the art of making laminates ofcellulosic substrates, it has long been appreciated that phenol-aldehyderesins tend to produce laminates of cellulosic materials which haverelatively poor cold punchability characteristics, that is to say, theresulting laminates crack and split and otherwise deteriorate in theregion where an impact force is used to cut or punch or otherwisepenetrate the surface of the resulting laminate construction.

l-leretofore, attempts have been made to use plasticizers in combinationwith phenol-aldehyde resins to improve cold punchability characteristicsin laminates, but the results have sufiered from a number ofdisadvantages. For example, even though cold punchability was achieved,the resulting laminates frequently had undesirably high water absorptionand undesirably low flexural strength.

it has now been discovered that a certain combination of phenol-aldehyderesole resin and carboxylated alkadiene interpolymer can be used toproduce laminates incorporating cellulosic substrates in sheetlike formwhich not only have desirable water absorption and flexural strengthcharacteristics, but which also have excellent cold punchabilitycharacteristics. This combination of normally thermoplastic interpolymerand thermosettable resin is typically in the form of an aqueous systemin which the resole resin portion is dissolved while the carboxylatedalkadiene interpolymer portion is suspended in the form of a latex. Thecombination is unusual because it is water dilutable or organic liquiddilutable. The combination is also unusual because it can be applied toa cellulosic substrate in a prelamination impregnation step in a singlepass operation thereby avoiding a two-step impregnation sequence.

By controllably advancing this combination when impregnated intocellulosic sheets to a predetermined extent before such are laid uptogether to produce a laminate under heat and pressure, one obtains thedesired cold punchable product laminates.

As those skilled in the art appreciate, cold punchable laminates haveuse in a variety of applications, for example, in household applianceand terminal boards, structural parts, electrical switches, instrumentpanels, insulating washers, switch parts, jack spaces and so forth.

SUMMARY This invention is directed to substantially nonporous coldpunchable laminate constructions having low water absorption and highflexural strength characteristics. Such laminate constructions employ aplurality of cellulosic sheet members arranged face to face in a layeredsequence. The sheet members are each impregnated with a homogeneousliquid composition of phenol-aldehyde resole resin and carboxylatedalkadiene interpolymer and this same mixture is used as the adhesivewhich binds together the individual sheet members into the desiredlaminate configuration. A resulting laminate construction issubstantially nonporous (as measured, for example, using a so-calledGurley air-penneable viscosity measurement of 15 seconds using a S-ouncecylinder and a 54-inch orifice). The invention is further directed tomethods for making such cold punchable laminate constructions fromcellulosic substrate members impregnated with a composition ofphenolaldehyde resole resin and carboxylated alkadiene interpolymer.

The liquid composition of phenol-aldehyde resole resin and carboxylatedalkadiene interpolymer used for impregnating cellulosic substrates inaccordance with the teachings of this invention comprises at the time ofuse for this invention from about 5 to 70 weight percent total combinedweight of the combination of resin and interpolymer with the balance upto 100 weight percent of any given such composition being a combinationof water and an organic liquid. The resin is dissolved in the liquidwhile the carboxylated alkadiene interpolymer is suspended in theaqueous phase as a latex (e.g. a colloidal suspension of polymerparticles).

On a percent solids basis, the combination of phenolformaldehyde resincomprises from about 35 to 75 weight percent of phenol-formaldehyderesin and, correspondingly, from about 25 to 65 weight percent of thecarboxylated alkadiene interpolymer, there being approximately 100 partsby weight total solids basis of combined weight in any givencomposition. The liquid portion of the composition comprises at leastabout 5 weight percent water (total liquid basis) with the balance up to100 weight percent of any given such liquid optionally having at leastone water-miscible organic liquid. Preferably, the liquid portion is 100percent water (total liquid basis). Examples of preferred organicliquids includes lower alkanols and lower alkanones. The term lower" asused herein has reference to molecules containing less than about 50carbon atom per molecule. Any inert (as respects resin and interpolymer)water miscible (partially or fully) organic liquid can be employed.

The phenol-aldehyde resole resin used in the present invention isconveniently separately prepared and has a phenol to formaldehyde mo]ratio of from about 0.9 to 2.5 and is produced by reacting under aqueousliquid phase conditions phenol with formaldehyde preferably in thepresent of a basic catalyst (preferably organic) to produce a solutioncontaining phenol-formaldehyde resinous condensation product. Suchresins having a low molecular weight are preferred, especially thosewhich can be prepared in the form of at least a 55 weight percentaqueous solution. Such a resin solution characteristically has a waterdilutability of at least about 1:], and preferably of at least 8:1. Inaddition, this resin has a free formaldehyde content which is less thanabout 5 weight percent. Preferably, the phenol-formaldehyde mol ratio inthis resin ranges from about 1% to 2. An organic basic catalyst ispreferably used in preparation as indicated so as to produce a resoleresin product which will not contain free ions which might conduct anelectrical charge after the resin has been thermoset. Suitable organicbasic catalysts are well known to the art; examples includetriethylamine, hexamethylenetetramine, and the like. Such resins arewell known to those skilled in the art.

The carboxylated alkadiene interpolymer used in the preparation of thelaminate constructions of this invention is one which is convenientlyseparately prepared in the form of a latex in water. Suitablecarboxylated alkadiene interpolymers are prepared by polymerizing amonomer mixture comprising from about 3 to 8 weight percent of acrylicacid, from about 35 to 60 weight percent of a conjugated alkadienemonomer, and the balance up to 100 weight percent of any given suchmonomer mixture comprising at least one material selected from the groupconsisting of monovinyl aromatic compounds and alkene nitrile compounds.A minor amount of a surfactant is added to the monomer mixture beforepolymerization. These latices and methods for their preparation aredescribed in the literature; see, for example, Bovey et al. in EmulsionPolymerization, published by Interscience Publishers, Inc. 1955 andSchildknecht in Polymer Processes" published by lnterscience Publishers,Inc. 1956. Optionally, such an emulsion may have chemically incorporatedthereinto through polymerization a small quantity, say, less than about2 weight percent based on total interpolymer weight of a divinylaromatic compound such as divinyl benzene, or the like.

Suitable monovinyl aromatic compounds include styrene (preferred);alkyl-substituted styrenes, such as ortho-, meta-, and paramethylstyrenes, 2,4-dimethyl styrene, paraethylstyrene, or alpha-methylstyrene; halogen substituted styrenes such as ortho-, meta-, andparachlorostyrenes, or bromostyrenes, 2,4-dichlorostyrene; and mixedhalogen plus alkylsubstituted styrenes, such as2-methyl-4-chlorostyrene; vinyl naphthalene; vinyl anthracene; mixturesthereof, and the like. The alkyl substituents generally have less thanfive carbon atoms, and may include isopropyl and isobutyl groups.

Suitable alkene nitrile compounds include acrylonitrile (preferred),methacrylonitrile, ethacrylonitrile, mixtures thereof, and the like.

Suitable conjugated alkadiene monomers include butadiene,3-methyl-l,3-butadiene, 2 methyl-l, 3 butadiene, piperylene,chloroprene, mixtures thereof and the like. Conjugated l,3 dienes arepreferred.

Such a latex suitable for use in making a composition for employment inthe present invention can contain typically as made from about 30 to 70parts by weight of total carboxylated alkadiene interpolymer with thebalance up to 100 weight percent being substantially water. Preferably,such a latex contains from about 45 to 60 parts by weight of suchinterpolymer.

To prepare a composition of phenol-aldehyde resin and carboxylatedalkadiene interpolymer, one simply admixes the respective materialstogether. As initially prepared, the resulting composition typically hasa total solids content (combined weight of carboxylated alkadieneinterpolymer and phenolformaldehyde resole resin) ranging from about 40to 70 weight percent. Conveniently, as prepared, the liquid phase of theresulting mixture is substantially entirely water.

However, before such mixture is used for impregnation of paper, it isconvenient to dilute the same with a water miscible organic liquid sothat the total solids concentration typically ranges from about 20 to 60weight percent, with solids contents of about 30 to SO'percent beingpreferred. A primary reason for adding such an organic liquid to theaqueous mixture is to permit one to impregnate paper without causing adeterioration in the wet strength of a cellulosic material such as paperwhich would occur before the evaporation of the water can beeffectuated. By adding in with the water an organic solvent, the wetstrength of a preformed cellulosic material after impregnation andbefore drying to remove volatile liquid is maintained at acceptableprocessing levels for subsequent drying, advancing, etc. by machines,etc. of the resulting impregnated sheet before or during the process ofmaking a laminate construction of the invention.

it will be appreciated that when such an aqueous mixture is used toimpregnate fibers 'not yet formed into a nonwoven sheet of cellulosicmaterial (woven or nonwoven) that the mixture may not necessarilycontain any organic liquid.

In general, an individual cellulosic substrate used in the laminates ofthe present invention is an integral performed sheetlike member composedsubstantially of cellulose fibers in a woven, nonwoven, or mixedstructure. Typical thicknesses range from about 3 to 30 mils (underabout l being preferred). Such members are well known to the art andinclude paper and cloth broadly; they need have no specialcharacteristics. The cellulosic fibers used in such a substrate membercan be of natural or synthetic origin and the sheet member can be in awoven or nonwoven state. Typical wellknown sources for cellulose fibersinclude wood, cotton, and the like. Typically, average cellulosic fibersused in substrates employed in this invention have length to widthratios of at least about 2: l and preferably about 6:1, with maximumlength to width ratios being variable.

The term substantially as used herein in reference to cellulose fibershas reference to the fact that a substrate comprises mainly cellulosefibers with not more than about to 10 percent of any given cellulosicsubstrate being other components, such as nonfibrous fillers, diluents,and the like, or fibrous noncellulosic materials, such as those derivedfrom organic sources (eg protein, synthetic organic polymeric fiberslike polyesters, etc.) or inorganic sources (e.g. silicious fibers ormetallic fibers). Such other components when and if present,characteristically have size ranges which are not greater in magnitudethan the cellulosic fibers. Preferably such other components are under 1weight percent of the total weight of a starting individual cellulosicsubstrate member.

Particularly when high electrical properties are desired in a productlaminate of the invention, the cellulosic substrate member should have alow ash content. Ash contents under 1 weight percent (based on totalcellulosic substrate member weight) are preferred, and those having ashcontents under 0.5 weight percent are preferred.

Typically, such sheet members contain impregnated thereinto from about40 to 60 weight percent of such a composiuTon of phenol-aldehyde resinand carboxylated alkadiene interpolymer (dry weight basis and based onweight percent of the substrate member). The so-impregnated substratemembers generally have thicknesses of less than about 10 mils butthicknesses up to 25 mils or even greater can be employed withoutdeparting from the spirit and scope of the present invention. ingeneral, a preferred range of thicknesses for such members is from about4 to 10 mils.

Preferably, the intermediate substrate sheer members can be made from acomposition of phenol-aldehyde resin and carboxylated alkadieneinterpolymer by impregnating a preformed cellulosic sheet member withsuch composition using any conventional means including spraying,coating, dipping, or the like, afier which it is convenient to dry thesotreated sheet to residual volatile content to less than about 15weight percent, preferably less than about 10 weight percent to leave animpregnated product having a desired volatile content.

When impregnating a preformed cellulosic sheet member with aphenol-aldehyde resin/carboxylated alkadiene interpolymer composition,it is convenient to use a composition which is not 100 percent water asrespects its liquid portion because, as those skilled in the artappreciate, water tends to injure the wet strength of the preformedsheet member. Conventionally, therefore, the art tends to mix with thecarboxylated alkadiene interpolymer and phenol-aldehyde resin mixturenot only water (as indicated above) but also a water miscible organicliquid because such a liquid of water and inorganic liquid tends tomaintain a high wet strength with paper impregnated with such acomposition.

In general, the cellulosic substrate sheet members so-impregnated withthe composition of phenol-aldehyde resin and carboxylated alkadieneinterpolymer are advanced by heating in air at a temperature of fromabout 30 to C. until the individual impregnated cellulosic substratemembers have a flow in the range of from about 3 to 20 weight percent.

For the purpose of this invention, flow of an impregnated cellulosicsheet member is detennined by pressing 2-inch inch discs (six ply) for 5minutes at 150 C. and 1000 p.s.i. and calculating the weight percent ofresin exuded from the discs.

Thereafter, the resulting so-advanced impregnated cellulosic sheetlikemembers are stacked or arranged into a desired layered sequence. Asthose skilled in the art will appreciate, an individual laminateconstruction of the invention can comprise a series of differentimpregnated cellulosic substrate members or a series of similar suchmembers depending upon properties desired in the product laminate.Preferably, all laminate layers contain the resin mixture of theinvention.

Following such an arranging of individual sheet member into a deck orlayered sequence, the deck or layered sequence is compressed topressures in the range of from about 50 to 2000 p.s.i. and heatedsimultaneously to temperatures from about l20-180 C. for a total timeinterval sufficient to substantially completely therrnoset thecomposition or phenol-aldehyde resole resin and carboxylated alkadieneinterpolymer. The product is in the form of a substantiallynonporousshaped article of manufacture which comprises at least two suchabove described impregnated cellulosic substrate sheet members. Theproduct laminates are cold punchable, as conveniently measured by ASTMtest procedure No. D617.

EMBODIMENTS The following examples are set forth to illustrate moreclearly the principles and practices of this invention to one skilled inthe art, and they are not intended to be restrictive but merely to beillustrative of the invention herein contained. Unless otherwise statedherein, all parts and percentages are on a weight basis.

Examples of low molecular weight phenol-aldehyde resole resins havingcharacteristics as described above and suitable for use in thisinvention are as follows:

EXAMPLE A Phenol (100 parts) 50 percent formalin (111 parts), andtriethylamine (five parts) are charged to a vessel. The resultingmixture is reacted at about 70 C. until the free formaldehyde content isless than about 4 percent, after which the mixture is cooled. Theproduct is a low molecular weight water soluble phenol-formaldehyderesole resin.

EXAMPLEB EXAMPLE C Phenol (100 parts), 50 percent formalin (128 parts)and triethylarnine (five parts) are charged to a vessel. The resultingmixture is reacted at about 70 C. until the free formaldehyde content isless than about 4 percent, after which the mixture is cooled. Theproduct is a low molecular weight water soluble phenol-formaldehyderesole resin.

Examples of carboxylated alkadiene interpolymer suitable for use in thisinvention are:

EXAMPLE D A commercially available latex comprising an interpolymer ofstyrene, butadiene and about 4-6 weight percent acrylic acid and having48 percent by weight of solids colloidally dispersed in an aqueousmedium known as Dow 636 latex.

EXAMPLE E A pressure vessel is charged with water (140 parts), styreneparts), butadiene parts), acrylic acid (five parts), Triton X-770 (twoparts), Triton X-lOO (one part), sodium bisulfate (0.10 part) andpotassim persulfate (0.25 part). The 50 persulfate and bisulfate areadded incrementally during the reaction. After heating 50 C. for 30hours, the latex is vacuum stripped to 50 percent solids. The product isa styrene/butadiene/acrylic acid interpolymer.

EXAMPLE F EXAMPLE (3-? To prepare the impregnating compositions of thisinvention,

a specific resole resin and a specific interpolymer are simply mixedtogether with stirring. Table 1 below gives examples of thesecompositions prepared from examples A-F.

TABLE I Carboxylated alkadiene Resole interpolymer Exam- Example No.Amount ple No. Amount Testing composition:

G 65 D 35 50 D 50 65 E 35 66 F 35 66 D 35 65 E 35 65 F 35 65 D 36 65 E35 66 F 35 The above compositions are diluted to 50 percent total solidsusing methanol.

Examples of laminate constructions of this invention made using treatingcompositions G through P above are prepared as follows:

EXAMPLES l-l5 Examples of preformed cellulosic substrate types arechosen as follows:

Type 1 Nonwoven linters paper about 10 mils in thickness, Type 2Nonwoven unbleached Kraft paper about 7 mils in thickness, Type 3Nonwoven alpha-cellulose paper about 10 mils in thickness, Type 4Nonwoven bleached Krafi paper about 15 mils in thickness, Type 5 Wovencotton duck cloth about 8 ounces weight, Type 6 Woven linen cloth about4 ounces weight. All types have an ash content less than about 0.9weight percent.

The impregnation procedure for impregnating each above substrate type isas follows:

Cellulosic sheets are passed through the impregnating solution (exampleG), drawn between squeeze rolls to remove excess resin and hung in anoven at C. for drying. A resin content of 50 percent is thus obtained ineach sample sheet so treated or otherwise as shown in table II below:

Laminates are made from these impregnating sheets by stacking togetherthese sheets in the form of eight-ply green laminates. Each greenlaminate is then cured using a pressure of 1500 p.s.i., a temperature offrom about C. and a time of about 15 minutes. The resulting laminatesare cold punchable without deleterious cracking when cold punched at 25C. according to ASTM D-6l7. The results are shown in table II below:

What is claimed is: W 1. A cold punchable substantially nonporouslaminate construction having low water absorption and high flexuralstrength comprising an integral combination of at least two cellulosicsubstrate sheet members arranged face-to-face in a layer sequence, eachsheet member being impregnated with, and adhered to the adjoining layerby a thermoset composition comprising a phenol-aldehyde resole resin anda carboxylated allradiene interpolymer comprising a polymerized monomermixture of from about 3 to 8 weight percent acrylic acid, from about 35to 60 weight percent of a conjugated alkadiene monomer, and the balanceup to 100 weight percent comprising at least one material selected fromthe group consisting of monovinyl aromatic compounds and alkene nitrilecompounds, said laminate construction having been prepared by the stepsof: V V V 7 A. heating cellulosic substrate sheet members eachimpregnated with a composition comprising phenol-aldehyde resole resinand carboxylated alkadiene interpolymer such that said individualcellulosic sheet members contain from about 30 to 70 weight percent ofsaid composition for each 100 parts by weight of said cellulosic sheetmember, said heating being conducted at a temperature of from about 30to 180 C. for a time sufficient to advance said composition to an extentsuch that each such sheet member has a flow of from about 3 to P E iL sWM B. arranging the resulting so-advanced cellulosic sheet member into adesired layered sequence, and

C. compreming the resulting sequence while maintaining pressures in therange of from about 50 to 200 p.s.i. while maintaining a temperature offrom about 120 to 180 C. for a time suflicient to substantiallycompletely thermoset said composition and thereby produce a desiredlaminate construction.

2t in a process for making a cold punchable substantially nonporouslaminate construction using cellulosic substrate sheet membersimpregnated with from about 30 to 70 weight percent of a compositioncomprising phenol-aldehyde resole resin and carboxylated alkadieneinterpolymer (dry weight basis) said interpolymer comprising apolymerized monomer mixture of from about 3 to 8 weight percent acrylicacid, from about 35 to 60 weight percent of a conjugated alkadienemonomer, and the balance up to lOO weight percent comprising at leastone material selected from the group consisting of monovinyl aromaticcompounds and alkene nitrile compounds, the improvement which comprisesthe steps of:

A. heating cellulosic substrate sheet members each impregnated with acomposition comprising phenol-aldehyde resole resin and carboxylatedalkadiene interpolymer such that said individual cellulosic sheetmembers contain from about 30 to 70 weight percent of said compositionfor each parts by weight of said cellulosic sheet member, said heatingbeing conducted at a temperature of from about 30 to 180 (2. for a timesufiicient to advance said composition to an extent such that each suchsheet member has a flow of from about 3 to 20 percent.

B. arranging the resulting so-advanced cellulosic sheet member into adesired layered sequence, and

C. compressing the resulting sequence while maintaining pressures in therange of from about 50 to 2000 psi. while maintaining a temperature offrom about to C. for a time sufficient to substantially completelytherrnoset said composition and thereby produce a desired laminateconstruction.

t i i

2. In a process for making a cold punchable substantially nonporouslaminate construction using cellulosic substrate sheet membersimpregnated with from about 30 to 70 weight percent of a compositioncomprising phenol-aldehyde resole resin and carboxylated alkadieneinterpolymer (dry weight basis) said interpolymer comprising apolymerized monomer mixture of from about 3 to 8 weight percent acrylicacid, from about 35 to 60 weight percent of a conjugated alkadienemonomer, and the balance up to 100 weight percent comprising at leastone material selected from the group consisting of monovinyl aromaticcompounds and alkene nitrile compounds, the improvement which comprisesthe steps of: A. heating cellulosic substrate sheet members eachimpregnated with a composition comprising phenol-aldehyde resole resinand carboxylated alkadiene interpolymer such that said individualcellulosic sheet members contain from about 30 to 70 weight percent ofsaid composition for each 100 parts by weight of said cellulosic sheetmember, said heating being conducted at a temperature of from about 30*to 180* C. for a time sufficient to advance said composition to anextent such that each such sheet member has a flow of from about 3 to 20percent. B. arranging the resulting so-advanced cellulosic sheet memberinto a desired layered sequence, and C. compressing the resultingsequence while maintaining pressures in the range of from about 50 to2000 p.s.i. while maintaining a temperature of from about 120* to 180*C. for a time sufficient to substantially completely thermoset saidcomposition and thereby produce a desired laminate construction.